1. Field of the Invention
The present invention relates to a vibration-type driving device (for example, a vibration wave motor), and more specifically, it relates to a vibration-type driving device that includes a vibrator vibrated by a piezoelectric body, the vibrator having a threaded portion formed thereon, and that includes a rotor engaged with the threaded portion and frictionally driven by vibration excited in the vibrator.
2. Description of the Related Art
In general, vibration-type driving devices are used, for example, for driving camera lenses and stages.
Some vibration-type driving devices have a vibrator and a moving body engaged with each other with threaded portions therebetween, and a piezoelectric element that excites vibration in the vibrator.
A conventional screw-driven vibration-type driving device will be described below (see, for example, Japanese Patent No. 4841432).
It includes a threaded shaft having an axis of rotation, and a nut engaged therewith. A piezoelectric element is fixed to the nut, and this piezoelectric element excites a primary bending vibration in the nut, in the direction of axis of rotation.
By exciting the orthogonal bending modes with a plus or minus 90-degree phase shift, a circular orbit is created, and the nut is moved in the orbital direction.
The threaded shaft can thereby be caused to simultaneously rotate and move in the axial direction.
In order to obtain a desired drive torque in a screw-driven vibration-type driving device such as that described in Japanese Patent No. 4841432, an appropriate frictional force needs to be generated between a vibrator such as the above-described nut and a moving body such as the above-described shaft, and therefore a pressing force needs to be applied.
However, the configuration described in Japanese Patent No. 4841432 has a problem that when the driving body or moving body is pressed by a spring component (pressure spring) or the like, and when the moving body moves in the axial direction, the pressing force changes with the moving distance thereof.